In recent years, there has been a significant increase in the number of rawindsonde-derived upper air parameters and indices used in evaluating severe weather and flash flood potential. For example, operational forecasters can quickly access over 35 such diagnostic tools using the computer-based Skew-T Hodograph Analysis and Research Program (SHARP) Workstation. SHARP also provides users with an excellent glossary section which gives concise explanations of all these indices and parameters along with references. This report can give additional help in fast-breaking convective situations. Section 2 is a table of 19 key indices and general warm-season values that has been compiled to serve as a time-saving fingertip guide for quickly diagnosing moderate and high potentials for severe weather and flash flood events.

This report recognizes the arbitrary and somewhat artificial nature of making such exact value stipulations as regional, seasonal, and synoptic-type variations also exist. Consequently, specific references are given in Section 3 for the index values chosen. Users are encouraged to review these references to gain a more complete understanding of the indices including their applicability and limitations in describing complex atmospheric processes. Subsequent regional, seasonal, and synoptic-type adjustments to table values are also encouraged.

This section explains how moderate potential values (MPV) and high potential values (HPV) for severe weather and flash flood events were chosen for each index. These MPV and HPV are general warm season values to be applied to soundings modified to forecast conditions near the times events may occur. Reference sources for each index and its MPV and HPV have been provided. Users should review these references to better understand how these indices can be applied as quick approximations to complex convective processes. The references often explain the limitations of using such approximations and may include information regarding MPV and HPV adjustments based on regional, seasonal, and synoptic-type variations.

KI: NOAA (1978, p. 4) and Funk (1991, p. 555) were sources for MPV (28) and HPV (38) when this index is used as a flash flood indicator. The MPV was a compromise between the NOAA (1978) recommendation of 24 and Funk (1991) recommendation of 30.

TEI: Moore (1992, p. 81) was the source for MPV (5ºC) and HPV (10ºC) assuming a cross-isentropic flow of 10 m/sec or greater. Elson (1991) has developed a program to determine TEI values in real-time using a personal computer.

CAP: Graziano and Carlson (1987, pp. 132-137) was the source for MPV (1-3ºC). A sounding with substantial instability, for example, B+ exceeding 1500 J/kg, capped by a small mid-level inversion can be favorable for an explosive energy release. However, Fig. 4 (p. 132) shows less than 15% of intense storms (radar reflectivity exceeding 50 dBZ) have a CAP exceeding 1.5ºC. The upper limit for severe storms was around 3ºC.

B-: MPV (25-75 J/kg) was inferred from Smith and Benjamin (1993, pp. 71-73) and Graziano and Carlson (1987, p. 128, Fig. 1). B- is the energy needed by parcels to reach the Level of Free Convection (LFC). Like CAP, B- is relevant only if instability is substantial, for example, B+ exceeds 1500 J/kg.

Smith and Benjamin (1993) examined a similar parameter called CIN (Convective Inhibition) for model-produced soundings near severe weather events. CIN was found to average 44 to 74 J/kg for tornadoes and 13 to 73 J/kg for large hail and damaging wind events. Calculations of B- for unstable soundings with mid-level capping inversions similar in shape to Graziano and Carlson (1987) Fig. 1 with a CAP strength of 2ºC yielded a typical B- of 20 to 40 J/kg.

PW: NOAA (1978, p. 4) was the source for MPV (130 percent of normal) and HPV (170 percent of normal). In addition, the National Meteorological Center Forecast Branch has found the precipitable water value of 1 inch (25 mm) or greater to be a useful criteria for diagnosing potential flash flood situations (Funk, 1991, p. 555).

SR HELICITY: Lazarus and Droegemeier (1990, p. 272, Fig. 2) was the main source for MPV (150 m2/sec2) and HPV (250 m2/sec2) to identify supercell situations. Davies-Jones et al. (1990, p. 590) was another source for MPV for identifying supercell situations and the main source for MPV and HPV for strong tornadoes. Later research (Johns and Doswell, 1992, p. 233) have corroborated these values. MPV (300 m2/sec2) identified F2 tornado intensity situations while HPV (450 m2/sec2) identified F4 tornado intensity situations. The storm inflow had to be 10 m/sec or greater.

EHI: Davies (1993b, p. 111, Table 4) and Hart and Korotky (1991, p. IV-3) were the sources for MPV (2) and HPV (4) for identifying mesocyclone and violent (F4-F5) tornado situations. This assumed a storm inflow of 10 m/sec or greater and a mid-level flow of 12 m/sec or greater.

Pulse-type thunderstorms have been generally associated with BRN less than 10. These BRN criteria work best when the B+ is between 1500 and 3500 J/kg (Weisman and Klemp, 1986) and the low and mid level environmental winds and storm relative inflow is 10 m/s or greater (Lazarus and Droegemeier, 1990).

SWEAT: Miller (1972, pp. F-2 and F-3) was the source for MPV (300) and HPV (400). MPV identified severe thunderstorm situations and HPV identified tornado situations. The 850 mb and 500 mb winds had to be 7 m/sec or greater.